Wireless Access

We have a couple of new 7240s running 6.3.1.2 code that have a SAP MTU setting of 1300.  Did the default size change from 1500?  These were set up by another tech so I am not sure if this was done during config or if the default setting has changed for some reason.

Is this in the AP sys profile?  Is there a value in that field in the UI?  

Yes, this is the AP System default profile.  Currently set to 1300.

So the default is blank which would be auto discovery of MTU size?

According to this post, default size is 1576 when field is left blank: http://community.arubanetworks.com/t5/ArubaOS-and-Controllers/Oversize-jumbo-frame-errors/m-p/5421/highlight/true#M1860

I see that it says it sends 1576 byte frames to detect if jumbo frames are supported, but it doesn't really address how it would determine MTU size if left blank.

I'm sure there's logic built into AOS that says if the value is blank than use a default value (I assume 1576 based on the link provided).  I can't find anything in the reference guides as conclusive proof, but I think you would find this to be true if you removed the current value and performed a packet capture where the AP is connected.

--- Edit ---

Just found the following command that should show you the SAP value.  You could try deleting the current value and then issue this command:

show ap debug received-config ap-name XXXXXX

Good call!  I have tested this and it does indeed default to 1500 when this field is left blank.